The immediate goal of this proposal is to define ultrastructurally the cytoskeleton of the specialized superficial lumenal cells of the mammalian urothelium. This knowledge will be applied to our overall objective which is to describe the early cellular changes relevant to the process of carcinogenesis. The intact, as well as extracted, epithelium will be examined by transmission electron microscopy to determine the types of cytoplasmic filaments and their relationship to the plasma membrane, the junctional complex and to specific cytoplasmic vesicles. These preparations will also be examined with high-voltage electron microscopy in order to describe from stereoscopic images the three-dimensional organization of the cytoplasm under normal conditions. These studies will form the basis for describing the cytoskeleton in cells derived from urothelial tissues poised at progressive stages of chemically-induced carcinogenesis.